Epidemiological and clinical features of non-multi-resistant methicillin-resistant Staphylococcus aureus (nmMRSA), multi-resistant methicillin-resistant S. aureus (mMRSA) and methicillin-sensitive S. aureus (MSSA) infections in tropical northern Australia

  • Steven Tong, Menzies School of Health Research, Charles Darwin University, Australia
  • Rachael Lilliebridge, Menzies School of Health Research, Charles Darwin University, Australia
  • Dr Emma Bishop, Menzies School of Health Research, Charles Darwin University, Australia
  • Dr Allen Cheng, Menzies School of Health Research, Charles Darwin University, Australia
  • Dr Deborah Holt, Menzies School of Health Research, Charles Darwin University, Australia
  • Dr Malcolm McDonald, Menzies School of Health Research, Charles Darwin University, Australia
  • Dr Bart Currie, Menzies School of Health Research, Charles Darwin University, Australia
  • Dr Craig Boutlis, Menzies School of Health Research, Charles Darwin University, Australia

    • Objectives
    Community-associated MRSA, with a non-multiresistant phenotype, has become increasingly common in northern Australia. We compared the epidemiology, clinical features and outcomes of nmMRSA with MSSA infections in the Top End in tropical northern Australia.

    Methods
    We determined regional incidence rates of S. aureus isolations using the microbiology database of hospitals in the Top End, and then conducted a case-control study to compare nmMRSA, MSSA, and mMRSA infections at the Royal Darwin Hospital.

    Results
    S. aureus was isolated from 2227 non-duplicate patients in the three Top End hospitals from April 2006 to April 2007; nmMRSA comprised 343 (15%), MSSA 1748 (79%), and mMRSA 136 (6%). The annual incidence of S. aureus and nmMRSA isolations was 1261 and 194 per 100,000 population respectively. Incidence rates significantly correlated with regional Aboriginal representation. In the case-control study we analysed data from 239 patients with nmMRSA, 478 with MSSA (controls) and 90 with mMRSA infections. Epidemiological, clinical and outcome profiles of patients with nmMRSA and MSSA infections were similar. Multivariate analysis showed female sex (OR 1.5) and residence in a rural region (OR 1.9) as significantly predictive of nmMRSA compared to MSSA infection. For nmMRSA infections, PVL status (OR 2.2) and the presence of at least one co-morbidity (OR 2.0) were the only variables significantly associated with systemic rather than localized infection.

    Conclusions
    There is a heavy burden of staphylococcal, including nmMRSA, infections in remote Aboriginal communities, probably reflecting the high prevalence of scabies, pyoderma, domestic crowding, and antibiotic usage. Severity of infection was associated with PVL status and co-morbidities rather than methicillin-resistance.